1. Field of the Invention
The present invention relates to an electrophotographic photoconductor useful in various electrostatic copying processes and devices for image forming (e.g., a copier, laser printer, etc.).
2. Discussion of the Background
Conventionally, as a photoconductive layer of an electrophotographic photoconductor for copiers and laser printers, a layer of selenium, selenium-tellurium, selenium-arsenic or amorphous silicon was used.
From a viewpoint of the structure of photosensitive layer, organic photoreceptors are classified into two types, that is, single-layer photoreceptors and multilayer photoreceptors.
The single-layer photoreceptors have a photosensitive layer that includes a charge generating material and a hole transporting material so that the single layer has both functions of a charge generating function and a charge transporting function.
The multilayer photoreceptor is a function-separated type photoconductor and includes a charge generation layer (CGL) and a charge transport layer (CTL) which are laminated. Both of single-layer photoreceptors and multilayer photoreceptors are practically used, but a charge transporting material with high electric charge mobility is demanded to achieve excellent sensitivity.
From the viewpoint of chargeability, the organic photoreceptors are classified into two types, that is, negatively chargeable photoreceptors and positively chargeable photoreceptors. Most charge transporting materials having high electric charge mobility are positively chargeable, so for actual use, negatively chargeable organic photoreceptors are major.
Photoreceptors are generally charged by corona discharge. As a large quantity of ozone is emitted by discharge, ozone pollutes room environment and photoreceptors tend to be deteriorated physically or chemically.
Filters for catching ozone were applied as an improvement, but the size of the apparatus becomes bigger and more complicated. On the other hand, other methods for charging that doesn't emit ozone are tried, but the process for electronograph becomes complicated.
Under this situation, positively chargeable photoreceptors that emit less ozone are demanded in the recent market, but for producing positively chargeable photoreceptors, an electron transport material having high electric charge mobility is required. So development of an electron transport material having not only high electric charge mobility but also low toxicity level and good compatibility with a binder resin is proceeding. Particularly, diphenoquinone compounds disclosed by Japanese patent No. 3778595 have excellent properties, so positively chargeable photoreceptors having the diphenoquinone compound provided an achievement in electrophotograph properties.
However, any positively chargeable photoreceptors that satisfy sensitivity of the photoconductor and durability when the photoconductor is used repeatedly have not yet been provided. Positively chargeable photoreceptors having a single photoconductive layer has a function of transporting both of electron and positive hole, and a function of charge generation as well. So a combination of each material, particularly combination of a hole transporting material and an electron transporting material is important. But the indication for choosing a hole transporting material and an electron transporting material was not clear. Photoconductor that includes a styryl compound is disclosed by examined published Japanese patent application No. H05-42611 (hereinafter referred to as JOP), but combination with diphenoquinone compound isn't disclosed.
Because of these reasons, a need exists for an electrophotographic photoconductor that satisfy high sensitivity and high stability.